Battery separator

ABSTRACT

A battery includes a separator with a trapping layer that traps dissolved metal ions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.10/682,740, filed on Oct. 9, 2003, now U.S. Pat. No. 7,914,920, which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to batteries.

BACKGROUND

Batteries, such as alkaline batteries, are commonly used as electricalenergy sources. Generally, a battery contains a negative electrode(anode) and a positive electrode (cathode). The anode contains an activematerial (e.g., zinc particles) that can be oxidized; and the cathodecontains an active material (e.g., manganese dioxide) that can bereduced. The active material of the anode is capable of reducing theactive material of the cathode. In order to prevent direct reaction ofthe active material of the anode and the active material of the cathode,the electrodes are electrically isolated from each other by a separator.

When a battery is used as an electrical energy source in a device, suchas a cellular telephone, electrical contact is made to the electrodes,allowing electrons to flow through the device and permitting therespective oxidation and reduction reactions to occur to provideelectrical power. An electrolyte in contact with the electrodes containsions that flow through the separator between the electrodes to maintaincharge balance throughout the battery during discharge.

SUMMARY

In one aspect, the invention features an alkaline battery with anelectrolyte, a cathode that includes an active material (e.g., a copperoxide), and a multilayer separator. The multilayer separator includes atrapping layer with a trapping component (e.g., a metal). In some cases,the cathode active material can dissolve in the electrolyte, formingdissolved metal ions (e.g., metal cations, polyatomic ions) that canlower the capacity and/or shelf life of the battery. The trapping layercan reduce and/or sorb the metal cation components of these dissolvedmetal ions, thereby enhancing the storage life and/or capacity of thebattery.

In one aspect, the invention features a battery. The battery has aseparator with a layer that includes a material that is capable ofreducing a metal cation component of a dissolved ion.

In another aspect, the invention features a battery. The battery has acathode that includes a copper oxide, an anode that includes zinc, and aseparator between the cathode and the anode. The separator has a firstlayer that includes cellophane, a second layer that includes bismuth, athird layer that includes zirconium dioxide, and a fourth layer thatincludes a non-woven material.

Other aspects, features, and advantages of the invention will beapparent from the drawing, description, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a battery.

FIG. 2 is a schematic view of an embodiment of a separator.

FIG. 3 is a schematic view of another embodiment of a separator.

FIG. 4 is a schematic view of a third embodiment of a separator.

FIG. 5 is a schematic view of a fourth embodiment of a separator.

DETAILED DESCRIPTION

Referring to FIG. 1, a battery or electrochemical cell 10 includes acylindrical housing 18 containing a cathode 12, an anode 14, and aseparator 16 between the cathode and anode. Cathode 12 includes anactive copper material (e.g., a copper oxide), and anode 14 includes anactive zinc material. Battery 10 also includes a current collector 20, aseal 22, and a metal top cap 24, which serve as the negative terminalfor the battery. Cathode 12 is in contact with housing 18, and thepositive terminal of battery 10 is at the end of the battery oppositefrom the negative terminal. An electrolyte is dispersed throughoutbattery 10.

In some cases, the electrolyte can dissolve the cathode active material(such as a copper material). For example, if the electrolyte is arelatively concentrated alkaline electrolyte (such as potassiumhydroxide), and if the cathode contains a copper material such as CuO,then the electrolyte can dissolve the copper material to form Cu(OH)₄ ²⁻ions. The Cu(OH)₄ ²⁻ ions can then diffuse to anode 14, where they formcopper metal and consume zinc:Zn+Cu(OH)₄ ²⁻→Zn(OH)₄ ²⁻+Cu  (1)As both the cathode active material and the anode active material areconsumed, the capacity of the battery decreases. In some cases, thecopper metal causes the evolution of hydrogen gas at anode 14, therebyincreasing the pressure within the battery and potentially causing thebattery to vent and leak. Furthermore, the copper metal can formdendrites that extend from the anode toward the cathode. The dendritescan penetrate the separator and contact the cathode, thereby shortcircuiting the battery. Consequently, the storage life of the batterycan be short and/or unreliable. Separator 16 is configured to limit orprevent contact between the anode active material and dissolved metalions from the cathode active material. Because of separator 16, battery10 may experience a reduced likelihood of short circuiting and/orgassing. As a result, battery 10 may be less likely vent and leak itsinternal contents. For these reasons and others, separator 16 canenhance the storage life and capacity of battery 10. Furthermore,separator 16 can achieve these advantages while being relativelynon-toxic and/or environmentally benign.

Separator 16 includes one or more selective membranes, trapping layers,and/or non-woven layers.

Referring to FIG. 2, separator 16 has a multilayer (i.e., more than onelayer) construction with a trapping layer 50 bonded on one side to aselective membrane 52, and on another side to a non-woven layer 54. InFIG. 2, selective membrane 52 is positioned by cathode 12, whilenon-woven layer 54 is positioned by anode 14.

As dissolved metal ions from the cathode active material travel throughtrapping layer 50, the trapping layer reduces and/or sorbs (e.g.,adsorbs and/or absorbs) the metal cation components of the dissolvedmetal ions. For example, the trapping layer can react with Cu(OH)₄ ²⁻ions (dissolved metal ions) to reduce copper (II) (the metal cationcomponent of the Cu(OH)₄ ²⁻ ions), thereby forming copper metal.Trapping layer 50 includes a solvent- and ion-permeable gel matrix, suchas poly(acrylic acid), poly(vinyl alcohol), poly(ethyleneoxide),poly(vinylpyrrolidone), poly(acrylamide), poly(vinyl butyral), orpoly(4-styrenesulfonic acid). Trapping layer 50 also includes one ormore (e.g., two, three, four, five) trapping components capable ofreducing and/or sorbing (e.g., adsorbing or absorbing) the metal cationcomponents of the dissolved metal ions. In some embodiments, trappinglayer 50 includes one trapping component, “TC1”, while in otherembodiments, trapping layer 50 includes two trapping components, “TC1”and “TC2”.

TC1 can be a metal (e.g., bismuth, tin, zinc, indium, cadmium, lead); ametal oxide (e.g., titanium oxide (TiO), an iron oxide (such as Fe₃O₄ orFeO), a niobium oxide (such as NbO or Nb0 ₂)); a metal hydride (e.g.,titanium hydride (TiH₂), zirconium hydride (ZrH₂), a misch-metal alloyhydride); or a salt (e.g., a metal salt, such as tin sulfide (SnS),bismuth sulfide (Bi₂S₃), iron sulfide (FeS)). In some cases, TC1 can bean organic material, such as an oxalate (e.g., magnesium oxalate(MgC₂O₄·2H₂O)) or a tartrate (e.g., bismuth tartrate (Bi₂(C₄H₄O₆·6H₂O)).In certain embodiments, TC1 is an organic complexing agent (e.g.,benzo-triazole, tolyl triazole). In some embodiments, TC1 can be ametalorganic material (e.g., zinc diethyldithiocarbamate).

Trapping component TC1 can have a reduction potential that is morenegative than the reduction potential of the metal cation component ofthe targeted dissolved metal ion. As a result, when TC1 comes intocontact with the dissolved metal ion, TC1 can reduce the metal cationcomponent of the dissolved metal ion to a metal. After reduction by TC1,the metal is insoluble and can be prevented from traveling to the anodeby one of the layers of the separator (e.g., the trapping layer, whichcan trap the metal). In some embodiments, trapping component TC1 has areduction potential that is from about ten millivolts to about 2,100millivolts negative to the reduction potential of the metal cationcomponent of the dissolved metal ion. In certain embodiments, TC1 has areduction potential that is from about 500 millivolts to about 1,500millivolts (e.g., about 600 millivolts) negative to the reductionpotential of the metal cation component of the dissolved metal ion(e.g., at pH 16). For example, if the dissolved metal ion is a speciesof silver (II) (e.g., Ag(OH)₄ ²⁻) originating from, e.g., a silver oxide(AgO) cathode, and trapping component TC1 is zinc, then at pH 16 thezinc can exhibit a reduction potential that is approximately 1,850millivolts negative to reduction potential of the metal cation componentof the dissolved Ag(OH)₄ ²⁻.

In some cases, TC1 has a reduction potential that is positive to thereduction potential of hydrogen (e.g., as measured in an electrolyte),such that TC1 may be unlikely to cause hydrogen gassing. For example,bismuth has a reduction potential that is positive (by approximately 400millivolts) to the reduction potential of hydrogen. Alternatively, TC1can have a reduction potential that is slightly negative to thereduction potential of hydrogen (e.g., as measured in an electrolyte).For example, TC1 can have a reduction potential that is from about onemillivolt to about 150 millivolts negative to the reduction potential ofhydrogen. Tin has a reduction potential that is slightly negative (byapproximately 100 millivolts) to the reduction potential of hydrogen. Inother cases, TC1 can have a reduction potential that is substantiallynegative to the reduction potential of hydrogen (e.g., as measured in anelectrolyte). For example, TC1 can have a reduction potential that isfrom about 150 millivolts to about 600 millivolts negative to thereduction potential of hydrogen. In such cases, TC1 preferably has ahigh hydrogen gas evolution overpotential (e.g., from about 500millivolts to about 750 millivolts of overpotential measured at a H₂evolution current density of one mA/cm² in alkaline electrolyte, such as6N KOH), so that TC1 will not cause hydrogen gas to evolve at anappreciable rate. For example, although zinc has a reduction potentialthat is about 500 millivolts negative to the reduction potential ofhydrogen (when both are measured in an alkaline electrolyte at a pH ofapproximately 16), zinc has a high overpotential for hydrogen gasevolution (about 720 millivolts at a current density of one mA/cm²).Thus, the actual rate of H₂ evolution from a zinc surface, at its restpotential, can be very low (e.g., about 0.02 microliter/hr/cm², asmeasured in 35.3% KOH with 2% dissolved ZnO at 60° C. and 760 torr).

Preferably, the product of the reaction between TC1 and the dissolvedmetal ion is relatively insoluble (e.g., from about 10⁻⁵ moles/liter toabout 10⁻³ moles/liter) in the electrolyte. In cases in which theproduct of the reaction between TC1 and the dissolved metal ion issomewhat soluble in the electrolyte, it is preferable for the reactionproduct not to detrimentally affect the active material of theelectrodes.

TC1 can be added to trapping layer 50 according to a number of differentmethods. For example, TC1 can be added to the trapping layer bydispersing a powdered version of TC1 within a gel matrix and applyingthe resultant gel or suspension to one of the sheet components of theseparator (e.g., the non-woven layer or the selective membrane). Asanother example, a dispersion of TC1 in a gel matrix can be prepared andcast or coated onto a release liner to form a layer. The layer can thenbe dried, stripped from the release liner, and adhered to one of thesheet components of the separator. As another example, a paint- orink-like dispersion of TC1 can be prepared and coated, printed orsprayed directly onto one of the sheet components of the separator. Insome embodiments, the above-mentioned gel coatings and/or paint- orink-like dispersions can also be used as adhesives that laminate thevarious layers of the separator together. As another example, TC1 can beformed on or in the trapping layer. For example, if TC1 is a metal, thenit can be formed on or in the trapping layer by, e.g., the chemical orelectrochemical reduction of a metal salt on or in the trapping layer.In such cases, TC1 can be formed on or in the trapping layer prior toassembly of the multilayer separator.

In some embodiments of separator 16, trapping layer 50 further includesanother trapping component. For example, when the reaction between TC1and the dissolved metal ion yields a soluble product (e.g., Bi₂O₃,Bi(OH)₃, or Bi(OH)₄ ⁻), then trapping layer 50 can include a secondtrapping component TC2. Trapping component TC2 is capable of reactingwith (e.g., sorbing) the soluble product to yield an insoluble product.In some cases, TC2, in its unreacted state, is relatively insoluble inthe electrolyte. For example, TC2 can have a solubility in theelectrolyte of from about 10⁻⁷ moles/liter (e.g., about 0.01milligrams/liter) to about 10⁻⁴ moles/liter (e.g., about tenmilligrams/liter). In other cases, TC2 is somewhat soluble in theelectrolyte (e.g., about 10⁻³ moles/liter or about 100milligrams/liter). Preferably, TC2 does not detrimentally affect theactive material of the electrodes. TC2 can be, for example, titaniumdioxide (TiO₂) or zirconium dioxide (ZrO₂). As an example, both titaniumdioxide and zirconium dioxide can absorb dissolved Bi(OH)₃ to formproducts which are insoluble in 9N KOH.

The trapping component or trapping components can have a relatively open(e.g., porous) structure. For example, the trapping component(s) can bein the form of a perforated foil or film, a woven mesh, a wire, and/or afilament. In some cases, the trapping component(s) can be in powderedform or can be dust.

The structure of the trapping layer can provide channels for ion and/orsolvent transmission. The trapping component(s) in the trapping layercan form a network that is not electronically conductive. The trappingcomponent(s) can be in the form of a relatively discontinuous networkthat includes, for example, metal particles surrounded by an adhesivepolymer matrix (such that the metal particles generally are not incontact with each other). The polymer matrix can be a gel which allowsfor permeation of electrolyte ions and electrolyte solvent.

In embodiments in which the trapping layer includes two differenttrapping components, TC1 and TC2, the trapping components can be admixedor can be independent from each other (e.g., located in separate regionsof the trapping layer). For example, in a trapping layer that includesboth bismuth metal and zirconium dioxide as trapping components, thebismuth metal and the zirconium dioxide can be admixed. Alternatively,the bismuth metal and the zirconium dioxide can be suspended in separatesub-layers of the trapping layer. For example, the bismuth metal and thezirconium dioxide can be suspended in adjacent sub-layers of a polymergel, with one sub-layer including primarily bismuth metal and the othersub-layer including primarily zirconium dioxide. In some embodiments,the bismuth metal is suspended primarily in a first polymer gel, whilethe zirconium dioxide is suspended primarily in a second, differentpolymer gel that is adjacent to the first polymer gel. The gel can beselected based on its compatibility with the trapping component(s) thatare used.

The trapping layer can have a thickness of from about one micron toabout 500 microns (e.g., about 65 microns). In some embodiments, thethickness of the trapping layer is from about 30 percent to about 70percent of the thickness of the entire separator.

Selective membrane 52 controls and/or limits the diffusion of dissolvedmetal ions from the cathode, thereby preventing the trapping layer frombeing inundated with dissolved metal ions over a short period of time.The electrolyte is generally able to travel through selective membrane52. The selective membrane can be, for example, cellophane or graftedpolyethylene. The thickness of the selective membrane can be from aboutten microns to about 40 microns (e.g., about 20 microns). In someembodiments, the thickness of the selective membrane is from about tenpercent to about 15 percent of the thickness of the entire separator.

Non-woven layer 54 is a fibrous membrane or fabric with good chemicaland/or mechanical properties. For example, the non-woven layer can haveone or more of the following properties: uniform thickness (e.g., 0.060mm±0.006 mm); uniform pore size; high tear strength; chemical stabilitytoward the cell electrolyte; chemical stability toward the anode and/orcathode active materials; high rate of electrolyte absorption (e.g.,greater than about 100 grams/m²); high rate of electrolyte permeationand diffusion; low ionic resistivity; and a low basis weight (e.g., lessthan about 30 grams/m²). The non-woven layer can provide support forseparator 16. Unlike selective membrane 52, non-woven layer 54 generallyis not selective with regard to dissolved ions. The non-woven layerconducts the electrolyte well, and thus can maintain a reservoir ofelectrolyte between the cathode and the anode. Non-woven layer 54 can bea fibrous polymer fabric (e.g., polyvinyl alcohol fibers and/or rayonfibers bonded with a polyvinyl alcohol binder). The thickness of thenon-woven layer can be from about 30 microns to about 120 microns (e.g.,about 60 microns). In some embodiments, the thickness of the non-wovenlayer is from about 25 percent to about 60 percent of the thickness ofthe entire separator. Separator 16 can be assembled according to anumber of different methods. In some embodiments, the trapping layer ofthe separator is assembled first. In certain embodiments, trapping layer50 is formed by blending powdered forms of the trapping component orcomponents (e.g., TC1 and TC2) with a polymer adhesive solution. Anexample of a polymer adhesive solution is a solution that includes apolyacrylic acid gelling agent (e.g., 5% Carbopol 934, available fromNoveon Inc.), an aqueous 25% poly(acrylic acid) solution (e.g., 20%Glascol E11, available from Ciba Specialty Chemicals), and 75% ethanol(or an aqueous solution of poly(vinyl alcohol)). After the trappingcomponent(s) have been blended with the polymer adhesive solution, themixture can be coated on a release liner (e.g., silicone coated Mylar).In some embodiments, trapping layer 50 can be formed by, e.g.,extrusion, or by blowing a powder-loaded thermoplastic polymer film. Insome cases, trapping layer 50 is formed by preparing a suspension of thetrapping component or components in viscose, and then extruding thesuspension into an acidic coagulating bath to form a regeneratedcellulose/trapping component composite.

After the trapping layer has been formed, it can be incorporated intoseparator 16. The trapping layer can be incorporated into the separatorby laminating it to the other layers of the separator. In some cases,the trapping layer is coated directly onto the non-woven layer and/orthe selective membrane (e.g., using a doctor blade). In certainembodiments, the trapping layer is separate from the non-woven layer.The trapping layer can hold the components of the separator together. Insome cases, the trapping layer is sprayed and/or printed onto one ormore of the other layers of the separator, such as the non-woven layer.

Preferably, dissolved metal ions are prevented from gaining accessaround separator 16. In some embodiments, the seams of separator 16 canbe glued together (e.g., with a hot-melt adhesive). In some cases, thebottom of the separator tube or cavity (i.e., the volume defined by theseparator in which anode 14 is placed) may be closed with an adhesiveseam. The bottom of the separator tube or cavity can be pinched orfolded together and sealed. In certain embodiments, a separate bottomcup can be formed and inserted into the separator tube, or the separatortube can be inserted into the bottom cup. The bottom cup can include thesame material and/or can have the same construction as the separator.The bottom cup can include any one or combination of the components ofthe separator, or can include a different material or materials from theseparator. The material or materials used to form the bottom cup can bepermeable or non-permeable. The seam between the bottom cup andseparator tube can be sealed by an adhesive. In some embodiments, aplastic resin plug can be cast into the bottom of the separator tube toeffect a closure. In some cases, the separator is formed of multiple(e.g., two, three, four) wraps of material.

Cathode 12 includes a conductive aid, a binder, and, as noted above, anactive material (e.g., a copper material). Examples of cathode activematerials include copper oxides (e.g., cupric oxide (CuO), cuprous oxide(Cu₂O)); copper hydroxides (e.g., cupric hydroxide (Cu(OH)₂), cuproushydroxide (Cu(OH))); cupric iodate (Cu(IO₃)₂); AgCuO₂; LiCuO₂;Cu(OH)(IO₃); Cu₂H(IO₆); copper-containing metal oxides or chalcogenides;copper chlorides (e.g., CuCl₂); and copper permanganates (e.g.,Cu(MnO₄)₂). The copper oxides can be stoichiometric (e.g., CuO) ornon-stoichiometric (e.g., CuO_(x), where 0.5≦×≦1.5). In someembodiments, cathode 12 includes from about 65 percent to about 99percent, preferably from about 75 percent to about 95 percent, and morepreferably from about 85 percent to about 95 percent, of copper materialby weight. All weight percentages provided herein are determined afterthe electrolyte has been dispersed. The copper material in cathode 12can include only copper oxide, or a mixture of copper materials. Forexample, of the copper material in cathode 12, the cathode can includefrom about five percent to about 100 percent by weight of copperchloride(s) and/or copper permanganate(s), with the remainder being,e.g., cupric oxide.

If cathode 12 includes a copper material, then the cathode can releaseCu(OH)₄ ²⁻ or Cu(OH)₄ ³⁻ ions into the electrolyte. The components ofthe trapping layer can react with the ions to form copper metal. Forexample, when trapping layer 50 includes bismuth, tin, or zinc, then thetrapping layer can react with Cu(OH)₄ ²⁻ ions according to the reactionsshown below:2Bi+3Cu(OH)₄ ²⁻→3Cu+Bi₂O₃+3H₂O+6OH⁻  (2)Sn+2Cu(OH)₄ ²⁻→2Cu+SnO₂+2H₂O+4OH⁻  (3)Zn+Cu(OH)₄ ²⁻→Cu+ZnO+H₂O+2OH⁻  (4)

When the trapping layer contains Fe₃O₄, then the trapping layergenerally will react with Cu(OH)₄ ²⁻ ions as shown below:2Fe₃O₄+Cu(OH)₄ ²⁻→Cu+3Fe₂O₃+H₂O+2OH⁻  (5)

A trapping layer that includes titanium hydride can react with Cu(OH)₄²⁻ ions as follows:TiH₂+3Cu(OH)₄ ²⁻→3Cu+TiO₂+4H₂O+6OH⁻  (6)

Tin sulfide generally will react with Cu(OH)₄ ²⁻ ions according to thereaction shown below:2SnS+2Cu(OH)₄ ²⁻→2Cu+SnS₂+SnO₂+2H₂O+4OH⁻  (7)

A trapping layer that includes an organic reducing agent, such as anoxalate or a tartrate, can react with Cu(OH)₄ ²⁻ ions to form coppermetal, as well as aldehydes, ketones, organic acids, carbon dioxide,carbonates and/or water.

While copper materials have been described, the cathode active materialneed not be a copper material. In some cases, the active material ofcathode 12 can be, for example, a silver compound (e.g., Ag₂O, AgO), apermanganate (e.g., KMnO₄, Ba(MnO₄)₂, AgMnO₄), a ferrate (e.g., K₂FeO₄,BaFeO₄), nickel oxide, nickel oxyhydroxide, cobalt oxyhydroxide, amanganese oxide, a bismuth oxide, or cobalt oxide. In general, thecathode active material can be any material that exhibits at leastpartial solubility (e.g., from about 10⁻⁷ mole/liter to about onemole/liter, about 10⁻⁶ mole/liter) in the system of which it is a part.Examples of cathode active materials are described in Provisional PatentApplication No. 60/503,667, filed on Sep. 16, 2003, and entitled“Primary Alkaline Battery Containing Bismuth Metal Oxide”, which ishereby incorporated by reference.

The conductive aid can increase the electronic conductivity of cathode12. An example of a conductive aid is graphite particles. The graphiteparticles can be any of the graphite particles used in cathodes. Theparticles can be synthetic or nonsynthetic, and they can be expanded ornonexpanded. In certain embodiments, the graphite particles arenonsynthetic, nonexpanded graphite particles. In these embodiments, thegraphite particles can have an average particle size of less than about20 microns, for example, from about two microns to about 12 mircons, orfrom about five microns to about nine microns as measured using aSympatec HELIOS analyzer. Nonsynthetic, nonexpanded graphite particlescan be obtained from, for example, Brazilian Nacional de Grafite(Itapecirica, MG Brazil (MP-0702X)). Alternatively or in addition, theconductive aid can include carbon fibers, described in commonly assignedU.S. Ser. No. 09/658,042, filed Sep. 7, 2000; and U.S. Ser. No.09/829,709, filed Apr. 10, 2001. In some embodiments, cathode 12includes from about one percent to about ten percent by weight of one ormore conductive aids.

Examples of binders include polyethylene powders, polyacrylamides,Portland cement and fluorocarbon resins, such as polyvinylidenefluoride(PVDF) and polytetrafluoroethylene (PTFE). An example of a polyethylenebinder is sold under the tradename Coathylene HA-1681 (available fromHoechst). Cathode 12 may include, for example, from about 0.1 percent toabout one percent of binder by weight.

In some embodiments, cathode 12 can be assembled without using a binderand/or without using carbon. In certain embodiments, cathode 12 can beassembled using reactive sintering. As an example of reactive sintering,a blend of 67 percent CuO and 33 percent copper powder is pressed in amold to create a pellet. The cathode pellet is then fired, in air, atabout 400° C. to about 600° C., resulting in a free-standing conductivecathode pellet. In some cases in which reactive sintering is used tomake a cathode, a portion of the copper powder can be replaced by fine,chopped copper fibers to, for example, provide a stronger and/or moreconductive cathode pellet.

Anode 14 can be formed of any of the zinc materials used in batteryanodes. For example, anode 14 can be a zinc gel that includes zinc metalparticles, a gelling agent, and minor amounts of additives, such asgassing inhibitor. In addition, a portion of the electrolyte isdispersed throughout the anode.

The zinc particles can be any of the zinc particles used in gel anodes.Examples of zinc particles include those described in U.S. Ser. Nos.08/905,254, 09/115,867, and 09/156,915, which are assigned to theassignee in the present application and are hereby incorporated byreference. The zinc particles can be a zinc alloy, e.g., containing afew hundred parts per million of indium and bismuth. Anode 14 mayinclude, for example, from about 67 percent to about 80 percent of zincparticles by weight.

Examples of gelling agents include polyacrylic acids, grafted starchmaterials, salts of polyacrylic acids, polyacrylates,carboxymethylcellulose or combinations thereof. Examples of suchpolyacrylic acids are Carbopol 940 and 934 (available from Noveon Inc.)and Polygel 4P (available from 3V), and an example of a grafted starchmaterial is Waterlock A221 (available from Grain Processing Corporation,Muscatine, Iowa). An example of a salt of a polyacrylic acid is AlcosorbG1 (available from Ciba Specialties). Anode 14 may include, for example,from about 0.1 percent to about one percent gelling agent by weight.

Gassing inhibitors can be inorganic materials, such as bismuth, tin,lead and indium. Alternatively, gassing inhibitors can be organiccompounds, such as phosphate esters, ionic surfactants or nonionicsurfactants. Examples of ionic surfactants are disclosed in, forexample, U.S. Pat. No. 4,777,100, which is hereby incorporated byreference.

Anode 14 can include other materials. For example, in some embodiments,anode 14 can include metals capable of reducing a cathode containing acopper material. Suitable metals include, for example, aluminum,magnesium, calcium, silicon, boron, titanium, zirconium, hafnium,lanthanum, manganese, iron, cobalt, chromium, tantalum, or niobium.Binary, ternary, quaternary and other multi-component alloy combinationsof these metals, and also those combinations including zinc with thesemetals, can be used.

The electrolyte can be any of the electrolytes used in batteries. Theelectrolyte can be aqueous or non-aqueous. An aqueous electrolyte can bean alkaline solution, such as an aqueous hydroxide solution, e.g., LiOH,NaOH, KOH, or a mixture of hydroxide solutions (e.g., NaOH/KOH). Forexample, the aqueous hydroxide solution can include from about 33percent to about 40 percent by weight of the hydroxide material, such asabout 9 N KOH (about 37 weight percent KOH). In some embodiments, theelectrolyte can also include up to about four percent by weight of zincoxide, e.g., about two percent by weight of zinc oxide.

In some embodiments, the electrolyte can be an aqueous salt solution(e.g., ZnCl₂, NH₄Cl, a mixture of ZnCl₂ and NH₄Cl, ZnSO₄, Zn(ClO₄)₂,MgBr₂, Mg(ClO₄)₂).

In some cases, the electrolyte can include a salt (e.g., Li-triflate(tri-fluoro-methyl-sulfonate)) dissolved in a non-aqueous solvent (e.g.,a mixture of dimethoxy ethane, ethylene carbonate, and propylenecarbonate).

The electrolyte can include other additives. As an example, theelectrolyte can include a soluble material (e.g., an aluminum material)that reduces (e.g., suppresses) the solubility of the cathode activematerial in the electrolyte. Electrolyte additives are described incommonly assigned U.S. Ser. No. 10/382,941, filed Mar. 6, 2003, theentire contents of which are incorporated by reference herein.

Housing 18 can be any housing commonly used in batteries, e.g., primaryalkaline batteries. In some embodiments, housing 18 includes an innermetal wall and an outer electrically non-conductive material such asheat shrinkable plastic. Optionally, a layer of conductive material canbe disposed between the inner wall and cathode 12. The layer may bedisposed along the inner surface of the inner wall, along thecircumference of cathode 12, or both. This conductive layer can beformed, for example, of a carbonaceous material. Such materials includeLB1000 (Timcal), Eccocoat 257 (W. R. Grace & Co.), Electrodag 109(Acheson Colloids Co.), Electrodag 112 (Acheson) and EB0005 (Acheson).Methods of applying the conductive layer are disclosed in, for example,Canadian Patent No. 1,263,697, which is hereby incorporated byreference.

Current collector 20 can be made from a suitable metal, such as brass.Seal 22 can be made, for example, of nylon.

Battery 10 can be assembled using conventional methods. In someembodiments, cathode 12 can be formed by a pack and drill method,described in U.S. Ser. No. 09/645,632, filed Aug. 24, 2000.

In some cases, battery 10 can include a hydrogen recombination catalystto reduce in the cell the amount of hydrogen gas, which can begenerated, for example, when copper metal is plated and zinc isoxidized. Suitable hydrogen recombination catalysts are described, e.g.,in U.S. Pat. Nos. 6,500,576, and 3,893,870. Alternatively or inaddition, battery 10 can be constructed to include pressure-activatedvalves or vents, as described, e.g., in U.S. Pat. No. 5,300,371.

Battery 10 can be, for example, a AA, AAA, AAAA, C, or D battery. Inother embodiments, battery 10 can be non-cylindrical, such as coin cell,button cells, prismatic cells, or racetrack shaped cells. Battery 10 caninclude a multi-lobed electrode, as described in U.S. Ser. No.09/358,578, filed Sep. 21, 1999.

The following examples are illustrative, and are not intended to belimiting.

EXAMPLES Example 1

A battery separator with a bismuth trapping layer was prepared asfollows.

Bismuth powder (-325 mesh, i.e. <45 μm particle size) was dispersed in apoly(acrylic acid)/ethanol/water solution with a high speed disperser.The loading of the bismuth was targeted to result in a composition thatwas 20 percent by volume bismuth powder and 80 percent by volumepolymer.

The viscous mixture was coated onto a silicone-coated Mylar releaseliner using a 25 mil wet thickness draw-down applicator.

The material was dried under ambient conditions and removed from therelease liner to yield a 60 micron, free-standing film.

The trapping layer as prepared above was used to form a multi-layerseparator. The trapping layer was located in the middle of theseparator, with a selective membrane at one end and a non-woven layer atthe other end. The separator was assembled as follows.

A 54 micron poly(vinyl alcohol)-based non-woven fabric was wetted withwater.

The bismuth-poly(acrylic acid) film (the trapping layer) was sandwichedbetween a 23 micron cellophane sheet and the poly(vinyl alcohol)-basednon-woven fabric. The water in the non-woven fabric was sufficient totackify the bismuth powder-poly(acrylic acid) film. A soft rubber rollerwas then rolled along the films to form inter-layer contact.

The sandwich structure was dried under ambient conditions to yield amulti-layer separator with good inter-layer adhesion.

The copper-trapping performance of the multi-layer separator prepared asdescribed above was investigated in comparison with a conventionalalkaline separator. The materials were used to separate acopper-containing aqueous KOH electrolyte from a non-copper-containingelectrolyte.

After storage at 60° C. for two weeks, 13 ppm copper was determined tobe present in the initially non-copper-containing electrolyte by UV-Visspectroscopy when the solutions were separated by a conventionalalkaline separator. However, with the bismuth-containing multi-layerseparator, only four ppm copper was detected.

Example 2

A battery separator with a tin trapping layer was prepared as follows.

Tin powder (-325 mesh, i.e. <45 μm particle size) was dispersed in apoly(acrylic acid)/ethanol/water solution with a high speed disperser.The loading of the tin was targeted to result in a composition that was20 percent by volume tin powder and 80 percent by volume polymer.

The viscous mixture was coated onto a silicone-coated release linerusing a 25 mil wet thickness draw-down applicator. The material wasdried under ambient conditions and removed from the release liner toyield a 60 micron, free-standing film.

The trapping layer as prepared above was used to form a multi-layerseparator. The trapping layer was located in the middle of theseparator, with a selective membrane at one end and a non-woven layer atthe other end. The separator was assembled as follows.

A 54 micron poly(vinyl alcohol)-based non-woven fabric was wetted withwater.

The tin-poly(acrylic acid) film (the trapping layer) was sandwichedbetween a 23 micron cellophane sheet and the poly(vinyl alcohol)-basednon-woven fabric. The water in the non-woven fabric was sufficient totackify the tin powder—poly(acrylic acid) film. A soft rubber roller wasthen rolled along the films to form inter-layer contact.

The sandwich structure was dried under ambient conditions to yield amulti-layer separator with good inter-layer adhesion.

Example 3

A battery including a multilayer separator was prepared as follows.

Preparation of the Separator

A battery separator with a trapping layer that included both abismuth-containing sub-layer and a zirconia (zirconiumdioxide)-containing sub-layer was prepared according to the followingprocedure.

First, a dry film including bismuth was prepared. Using a high shearlaboratory mixer (from Silverson L4RT-A) at 5000 rpm, 25 grams ofCarbopol 934 were slowly added to 375 grams of ethanol. Next, 100 gramsof Glascol Ell were slowly added to the mixture, with continued mixing,until a homogeneous viscous solution was obtained. Then, 150 grams ofbismuth metal (-325 mesh, 99.5% metals basis) were slowly added to themixture, and mixing was continued until the mixture was homogeneous. Theviscous suspension was then coated in 6″ wide strips onto asilicone-coated Mylar release liner, using a film applicator. The resultwas a dry film with a thickness of 90 microns.

In a separate process that occurred while the dry film was beingprepared, a non-woven material including zirconia was prepared. Using ahigh shear laboratory mixer, 50 grams of zirconia nanopowder (fromAldrich Chemical Company) were dispersed in 500 grams of deionizedwater. Next, 38.46 grams of a 13% by weight poly(vinyl alcohol) [averagemolecular weight (Mw)=85,000−146,000, 87-89% hydrolyzed] solution wereslowly added to the dispersion with continued mixing. Then, 20 grams ofiso-propanol were added to the final dispersion, and a 54 micronpoly(vinyl alcohol)-based non-woven fabric sheet was taped to a releaseliner. The dispersion was then impregnated into the non-woven fabricsheet by pouring the dispersion onto the non-woven fabric sheet,removing excess solution by running a straight-edged plastic shim acrossthe surface of the non-woven fabric sheet, drying the non-woven fabricsheet at ambient temperature for one hour, and then repeating theprocess. Using a metal punch, 1.3 cm diameter circles were punched fromthe non-woven fabric. The non-woven fabric was dried at 60° C.Comparison to non-impregnated samples indicated a loading of 2.2×10⁻³grams ZrO₂-poly(vinyl alcohol) per square centimeter of non-wovenfabric.

Separator material was then prepared according to the followingprocedure. A sheet of 6″×8″ bismuth metal—poly(acrylic acid) film wasremoved from the release liner. The sheet was sprayed with a solution of75 wt. % ethanol−25% deionized water to tackify the film. The film wasthen placed on the top surface of a 6″×8″ sheet of 23 micron cellophanefilm. Thereafter, a 6″×8″ sheet of the non-woven fabric containingZrO₂—poly(vinyl alcohol) was placed on the free surface of the bismuthmetal—poly(acrylic acid) material. The layers were compressed andbrought into contact using a soft rubber roller. Subsequent drying underambient conditions yielded a separator with good interlayer adhesion.

A separator cup was then formed, according to the following procedure.Strips of the above separator material (4.6 cm×6.6 cm) were cut andconverted into a sealed separator cup. A 9.9 mm diameter hole wasdrilled in a PTFE block. Approximately 0.15 grams of molten hot-meltadhesive (Type 3748TC, from 3M) were placed at the bottom of the PTFEcavity. A separator strip was wrapped around a metal rod coated with adry film PTFE mold release coating (from Sprayon Products). Theseparator was folded inward (approximately one millimeter) at the bottomof the metal rod, and was then immersed into the molten hot-meltadhesive. The adhesive was allowed to cool, and the separator wasremoved from the PTFE mold. Subsequent removal of the metal rod yieldeda double-wrapped separator cup with a bottom seal.

Next, a battery was formed according to the following procedure. Acathode blend with the following composition was prepared in a smallblender: 89.3 percent by weight copper (II) oxide, 4.5 percent by weightexpanded graphite, 0.2 percent by weight Coathylene, and 6 percent byweight 9N KOH. Then, 22.9 grams of the blended cathode mixture werepacked into a conventional AA can. Portions of the cathode mixture wereadded sequentially to the can with intermediate pressing of the powderinside of the can. After final pressing, a cavity was formed throughoutthe central length of the cathode, using a 9.9 mm drill. An AA cell wasthen fabricated by inserting the sealed separator cup into the cathodecavity and adding approximately 1.2 grams of 9N KOH electrolyte andapproximately 5.6 grams of conventional zinc anode slurry. A sealassembly including a tin-plated brass current collector was placed intothe open end of the cell, with the current collector dipping into thezinc slurry. The cell was crimped shut.

Three AA cells were formed according to the above procedure. Afterfabrication, the open circuit voltage (OCV) of the cells wasapproximately 1.4 V. The three cells were then stored at 60° C. The OCVrapidly dropped to 1.1-1.0 V, but then the cells maintained an OCVof >1.0 V for >28 days storage at 60° C. Similar cells constructed withconventional cellophane-non-woven separators (Duralam DT225, fromDuracell, Aarschot, Belgium) failed within 48-72 hours.

Other Embodiments

Other embodiments are possible.

The separator can have different numbers of layers (e.g., two layers,three layers, four layers, five layers, six layers). In some cases, theseparator can have multiple trapping layers. The components of theseparator can be arranged in different ways. For example, and referringnow to FIG. 3, a separator 60 has a middle portion 56 including atrapping layer 50 bonded on one side to a non-woven layer 54. On itsother side, trapping layer 50 is attached to a selective membrane 52. Onits side that is not bonded to trapping layer 50, non-woven layer 54 isbonded to a second selective membrane 52′. As shown, selective membrane52 is positioned by cathode 12, while second selective membrane 52′ ispositioned by anode 14.

Second selective membrane 52′, like selective membrane 52, can controlthe diffusion of dissolved metal ions. It can also slow and/or limit thediffusion of products created by the trapping layer. Second selectivemembrane 52′ conducts the electrolyte well and can be, for example,cellophane or grafted polyethylene. In some cases, second selectivemembrane 52′ is identical to selective membrane 52, while in other casessecond selective membrane 52′ is different from selective membrane 52.For example, second selective membrane 52′ can be of a differentmaterial and/or thickness than selective membrane 52.

In FIG. 4, a separator 70 includes a trapping layer 50 between aselective membrane 52 and second selective membrane 52′. Selectivemembrane 52 is positioned by cathode 12, while second selective membrane52′ is positioned by anode 14. By having selective membranes on eitherside, trapping layer 50 of separator 70 can be prevented from becomingoverburdened with dissolved metal ions.

Referring now to FIG. 5, a separator 80 includes non-woven material 54surrounded on both sides by trapping layers 50 and 50′. Trapping layers50 and 50′ may be identical or different. Trapping layer 50 is attachedto selective membrane 52, while trapping layer 50′ is attached to secondselective membrane 52′. Selective membrane 52 is positioned by cathode12, while second selective membrane 52′ is positioned by anode 14.

By having two trapping layers 50 and 50′, separator 80 can exhibitenhanced trapping capability. As an example, when trapping layers 50 and50′ are similar or identical, soluble metal ions from the cathode whichescape through trapping layer 50 may still be absorbed by trapping layer50′. A separator with two trapping layers can achieve an efficient,cascading effect, in terms of its trapping capacity. For example, themain burden of dissolved metal ions can be absorbed by the firsttrapping layer (50), which may fail to trap a small fraction of theseions. Because the second trapping layer (50′) is faced with fewerdissolved metal ions, it may remain in a relatively pristine condition,such that it can efficiently trap the small quantity of dissolved ionsthat were not trapped by the first trapping layer (50).

In some embodiments, trapping layers 50 and 50′ are different from eachother. For example, in some cases (such as in FIG. 5), trapping layer 50is positioned between cathode 12 and trapping layer 50′. In such cases,trapping layer 50 can be designed to trap metal ions emanating fromcathode 12, while trapping layer 50′ can be designed to trap by-productions formed during ion trapping reactions that occur in trapping layer50. Alternatively or additionally, trapping layer 50′ can be designed todirectly trap dissolved metal ions that have escaped through trappinglayer 50.

As an example, when separator 80 is designed to trap Cu(OH)₄ ²⁻dissolved metal ions, trapping layer 50 can contain bismuth metalpowder, and trapping layer 50′ can contain, e.g., nano-particle ZrO₂. Intrapping layer 50, the following trapping reaction occurs:2Bi+3Cu(OH)₄ ²⁻→3Cu+Bi₂O₃+3H₂O+6OH⁻  (8)Bi₂O₃ generated in the above reaction is partially soluble in 9N KOHelectrolyte. Dissolved Bi₂O₃ will migrate out of trapping layer 50,toward both the cathode and the anode. In some cases, dissolved Bi₂O₃can cause hydrogen gassing to occur on a zinc anode. Trapping layer 50′can be used to avoid this problem by trapping the dissolved Bi₂O₃ beforeit reaches either the anode or the cathode. As an example, trappinglayer 50′ can include ZrO₂, such that it reacts with dissolved Bi₂O₃ asfollows:Bi₂O₃+ZrO₂→Bi₂O₃ .xZrO₂  (9)The product of the reaction between Bi₂O₃ and ZrO₂ is Bi₂O₃ ·xZrO ₂,which is an insoluble complex of Bi₂O₃+ZrO₂ (of an unknown composition).

In some cases, trapping layer 50′ further includes a second trappingcomponent capable of trapping the same dissolved metal ion that trappinglayer 50 is designed to trap. As an example, trapping layer 50′ caninclude an admixture of bismuth metal and ZrO₂. The bismuth metal cantrap dissolved Cu(OH)₄ ²⁻ ions that have gotten through trapping layer50, while the ZrO2 can trap Bi₂O₃, according to equation 9 above.

All references, such as patent applications, publications, and patents,referred to herein are incorporated by reference in their entirety.

Other embodiments are in the claims.

1. A battery, comprising: a cathode; an anode; an electrolyte; and aseparator comprising a first layer comprising metal particles; whereinthe electrolyte is an alkaline electrolyte and the metal particles arecapable of reducing a metal cation component of an ion generated fromthe cathode active material and dissolved in the electrolyte.
 2. Thebattery of claim 1, wherein the metal is bismuth, tin, zinc, or indium.3. The battery of claim 1, wherein the first layer has a thickness offrom about one micron to about 500 microns.
 4. The battery of claim 1,wherein a thickness of the first layer is from about 30 percent to about70 percent of a thickness of the separator.
 5. The battery of claim 1,wherein the battery further comprises a second layer that is adjacent tothe first layer.
 6. The battery of claim 5, wherein the second layercomprises a non-woven material.
 7. The battery of claim 5, wherein thesecond layer comprises cellophane or grafted polyethylene.
 8. Thebattery of claim 5, wherein the first layer is separated from the secondlayer by at least one other layer.
 9. The battery of claim 5, whereinthe separator further comprises a third layer.
 10. The battery of claim9, wherein the first layer is disposed between the second layer and thethird layer.
 11. The battery of claim 9, wherein the second layercomprises cellophane or grafted polyethylene.
 12. The battery of claim9, wherein the second layer comprises a non-woven material and the thirdlayer comprises cellophane or grafted polyethylene.
 13. The battery ofclaim 9, wherein the second layer is adjacent to the anode.
 14. Thebattery of claim 1, wherein the metal has a reduction potential that ispositive to the reduction potential of hydrogen.
 15. The battery ofclaim 1, wherein the cathode includes a cathode active materialincluding a copper material.
 16. The battery of claim 15, wherein thecathode active material includes a copper oxide or a copper hydroxide.17. The battery of claim 15, wherein the anode includes zinc and theelectrolyte includes potassium hydroxide and the dissolved ion inCu(OH)₄ ²⁻.